The present invention relates to an image reading apparatus, image reading method, and storage medium and, more particularly to, an image reading apparatus, image reading method, and storage medium, capable of reading an image, obtained by, e.g., an optical scanner, converting the image into electric image signals by an image sensor, digitizing the electric image signals by an analog-digital (A/D) converter, and transferring the digitized signals to an external device, and a user-friendly image reading apparatus, image reading method, and storage medium capable of obtaining image data of good quality by constantly performing optimum shading correction by reducing undesirable effects caused by, e.g., deterioration of a light source.
Conventionally, an image reading apparatus capable of transferring image data to a host computer is provided with a white shading correction board. Using the shading correction board, so called shading correction for correcting variation in various characteristics of optical sub-system and variation in output signals from respective photoelectric conversion elements of an image sensor, thereby eliminating reading irregularity (spots), is commonly performed. Shading correction data for each color component used in the shading correction is usually generated as data of a single line by operating acquired data of several lines.
Further, in a conventional image reading apparatus, an on-period of a light source, such as an LED, used for reading a standard white board for shading correction, and shading correction data obtained on the basis of the read data are transferred to a host computer in advance and, when reading an image, the on-period of the light source and the shading correction data used as a reference level, for instance, are loaded down from the host computer, then shading correction is performed, using the shading correction data, on image data obtained by reading an original image while turning on the light source for the on-period.
Further, in the conventional reading apparatus, various image processings, such as shading correction, are applied to electric signals generated by scanning the original image. The shading correction data is generated each time an original is read, or in response to a manual instruction by a user when the user determines on the basis of deterioration of quality of a read image that the shading correction is necessary.
An example of a conventional image reading apparatus is explained below.
FIG. 11 is a block diagram illustrating a brief configuration of an image reading apparatus, such as an image scanner. In the image reading apparatus, digital image data is generated by processing signals outputted by an image sensor 1041 and outputted to a host computer 1048, such as a personal computer.
The image reading apparatus includes the image sensor 1041 which scans an original with light, receives reflected light from the original, and converts the light into analog electric signals, an analog circuit 1042 which processes the analog signals outputted from the image sensor 1041, an analog-digital (A/D) converter 1043 for converting analog image signals outputted from the analog circuit 1042 into digital image signals, a digital processing circuit 1044 for applying predetermined digital signal processes to the digital image signals, RAM 1045 for storing the processed digital image data, a CPU 1046 for controlling the overall operation of the image scanner 1041, and an interface unit 1047 for controlling an interface with an external device (host computer, in this case), as shown in FIG. 11.
In the apparatus shown in FIG. 11, when a command for reading an original is inputted from the host computer 1048, the CPU 1046 controls the image sensor 1041 to read a reference board in advance of reading an image area of the original, generates reference data, and stores the reference data in the RAM 1045. Thereafter, the CPU 1046 performs predetermined calculation based on the reference data and generates shading correction data, and stores the data in the RAM 1045. Then, the reading of the image area of the original is initiated as well as read image is corrected using the shading correction data.
In a case where the image reading apparatus does not generate shading correction data each time an original is read, a command for generating shading correction data is provided in a software installed on the host computer 1048, and the user instructs to generate the shading correction data by operating the host computer 1048 when necessary.
However, in an image reading apparatus adopting a line sequential reading method, data of only one color component out of three color components, namely, red (R), green (G) and blue (B), is acquired by reading a single line (acquired data is called xe2x80x9cshading dataxe2x80x9d hereinafter); accordingly, in order to obtain shading data of all the three color components, it is necessary to scan an identical line three times. In addition, since it is necessary to acquire shading data of n lines (n is a positive integer, 2 or greater) for each color component, memory having a capacity of storing data of (n+1) linesxc3x973 color components, where xe2x80x9c1xe2x80x9d corresponds to data of calculation result, is needed for generating shading correction data. Further, in a case of sharing a memory area for storing acquired shading data of n lines and sequentially generating shading correction data of the respective colors, the required capacity of the memory for generating shading correction data is to store data of (n+3) lines, namely, n lines of data of a single color component and generated shading correction data of the respective three color components. In this case, a white shading board having an effective area width corresponding to 3xc3x97n lines is necessary, which requires a space for accommodating the board, and makes it difficult to reduce the size of an image sensing apparatus.
Further, there is a problem in which proper shading correction is not performed using shading data loaded down from the host computer when the quantity of light illuminating an original has been changed due to, e.g., deterioration of a light source.
Further, it is necessary to read a reference board or a white board and generate reference data, then perform predetermined calculation by a CPU using the reference data in order to generate shading correction data, and write the shading correction data in the RAM in advance of reading an image. Therefore, if the shading correction data is generated each time an image is read, it takes extra time for generating the shading correction data in addition to reading the original.
Especially, when reading a color image, it is necessary to generate image data of the respective R, G and B color components, therefore, for generating shading correction data for the respective R, G and B color components, it takes three times longer than time for generating shading correction data for a black-and-white image. Furthermore, when a high-density image sensor is used, since a large number of pixels are arranged in the sensor, it requires longer time to generate the shading correction data.
Accordingly, it is stressful for a user if shading correction data is generated each time an original is read since it takes a longer time for reading the original.
Meanwhile, in a case where a user instructs to generate shading correction data by operating a computer, the user must evaluate deterioration of image quality, which requires that the user have a skill of a certain level and perform extra work.
The present invention has been made in consideration of the above situation, and has as its object to provide an image reading apparatus, an image reading method, and a storage medium capable of outputting image signals to which shading correction has been applied using a minimum memory area and a white shading correction board of a minimum width.
According to one aspect of the present invention, the foregoing object is attained by providing an image reading apparatus comprising: illumination means for irradiating light on an object; photoelectric conversion means for receiving light from the object and converting the received light into electric signals; optical means for guiding the light from the illumination means to the photoelectric conversion means via the object; moving means for relatively moving a part or all of the object, the illumination means, the optical means, and the photoelectric conversion means to obtain scan image information; and shading correction means for correcting reading unevenness due to variation in characteristics of the illumination means, the optical means, and the photoelectric conversion means, wherein, when acquiring shading data used for generating shading correction data, a reference member having a uniform reflection density is used as the object, and the photoelectric conversion means reciprocally reads the light from the reference member by reversing a scanning direction while performing moving operation by the moving means.
In accordance with the image reading apparatus of the present invention as described above, the illumination means irradiates light of three primary colors of R, G and B, and, when acquiring the shading data of respective R, G and B components, the reference member is used as the object, and the photoelectric conversion means reciprocally reads the light from the reference member while light sources for irradiating the R, G and B light are sequentially turned on in synchronization with the reversal of the scanning direction by the moving means.
Further, in accordance with the image reading apparatus of the present invention as described above, an optical color filter for generating light of R, G and B components is provided on a light path from the illumination means, wherein, when acquiring the shading data of respective R, G and B components, the reference member is used as the object, and the photoelectric conversion means reciprocally reads the light, from the reference member sequentially illuminated by the light of R, G and B components in synchronization with the reversal of the scanning direction by the moving means.
According to another aspect of the present invention, the foregoing object is attained by providing an image reading apparatus which reads an object by irradiating light on the object while a sensor for reading an image scans the object in a predetermined direction, receiving light from the object and converting the light into electric signals, the apparatus comprising: shading correction means for correcting reading unevenness due to sensitivity variation on reading elements of the sensor; and control means for controlling scanning operation and reading operation of the sensor so as to reciprocally read an identical target data area while reversing a scanning direction of the sensor when acquiring shading data, used for generating shading correction data, by the sensor.
In accordance with the image reading apparatus of the present invention as described above, the light irradiated on the object is preferably light of three primary colors of R, G and B, and, when acquiring the shading data, the scanning operation is performed in a predetermined direction a same number of times as a number of the primary colors in response to turning-on operation of light sources of the respective colors.
Further, in accordance with the image reading apparatus of the present invention as described above, light irradiated on the object is light of three primary colors of R, G and B using a predetermined color filter, and, when acquiring the shading data, the shading data of the respective colors is sequentially read in synchronization with the scanning operation, corresponding to the respective colors, in the predetermined direction.
According to still another aspect of the present invention, the foregoing object is attained by providing an image reading method for reading an image of an object in which the object is illuminated while a sensor for reading an image scans the object in a predetermined direction, light from the object is received and converted into electric signals, the method comprising the steps of: correcting reading unevenness due to a sensitivity variation on reading elements of the sensor; and controlling scanning operation and reading operation of the sensor so as to reciprocally read an identical target data area while reversing a scanning direction of the sensor when acquiring shading data, used for generating shading correction data, by the sensor.
In accordance with the method of the present invention as described above, it is preferable to irradiate light of three primary colors of R, G and B on the object and perform the scanning operation in a predetermined direction a same number of times as a number of the primary colors in response to turning-on operation of light sources of the respective colors when acquiring the shading data.
Further, in accordance with the method of the present invention as described above, light of three primary colors of R, G and B is irradiated on the object, and, when acquiring the shading data, the shading data of the respective colors may be sequentially read in synchronization with the scanning operation, corresponding to the respective colors, in the predetermined direction.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to perform the respective means of any one of the image reading apparatuses as described above.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to execute any one of the image reading methods as described above.
In accordance with the present invention as described above, when light sources of the three primary colors, namely, R, G and B, are turned on, for instance, while moving an optical sub-system which includes the illumination means, the optical means, and photoelectric conversion means in the normal reading direction, the illumination means irradiates light onto a reference member and the photoelectric conversion means receives the reflected light from the reference member, and shading data of R component is obtained, first. Thereafter, the same area of the reference member illuminated for obtaining the shading data of R component is illuminated to obtain shading data of G component while moving the optical sub-system in the direction opposite to the normal reading direction. Then, shading data of B component is obtained while moving the optical sub-system in the normal reading direction again. After that, reading of an original is initiated. Each time the shading data of each color component is acquired, shading correction data of the color component is sequentially generated.
In the aforesaid manner, the required capacity of memory for generating shading correction data is to store n lines of acquired shading data of a single color component and shading correction data of a single line for each of the respective color components. In short, the required memory capacity for generating shading correction data is to store data of (n+3) lines.
Further, the optical sub-system reciprocally scans the reference member, such as a white shading correction board, to acquire the shading data of the R, G and B color components, thus, the reference member needs to have a width large enough to include n lines of area where the optical sub-system can scan. Accordingly, it is possible to reduce the size of the apparatus.
It is another object of the present invention to provide an image reading apparatus, an image reading method, and a storage medium, capable of performing proper shading correction when deterioration of a light source, which affects reading of image data, occurs.
According to one aspect of the present invention, the foregoing object is attained by providing an image reading apparatus capable of storing on-period data for a light source for irradiating light on an original and shading correction data for image data acquired by reading the original, in an external device, loading down the shading correction data from the external device at a beginning of image reading operation, and performing shading correction using the down-loaded shading correction data on the image data, the apparatus comprising: on-period control means for controlling an on-period of the light source in accordance with the on-period data down-loaded from the external device; reference member reading means for reading light from a reference member illuminated with the light from the light source; and comparison means for comparing a level of a read signal outputted from the reference member reading means to a reference level of the shading correction data loaded down from the external device.
According to another aspect of the present invention, the foregoing object is attained by providing an image reading apparatus including: photoelectric conversion means for converting light from an original illuminated with light from a light source into electric signals; shading correction means for applying shading correction on the electric signals outputted from the photoelectric conversion means; a reference member used for acquiring shading correction data used for the shading correction performed by the shading correction means; communication means for communicating with an external device; and transmission means for transmitting on-period data for the light source and shading correction data obtained by the shading correction means to the external device, the apparatus comprising:
correction data down-loading means for loading down the on-period data for the light source and the shading correction data set in the external device; on-period control means for controlling a turn-on/off operation of the light source on the basis of the on-period data loaded down by the correction data down-loading means; reference member reading means for reading the light from the reference member illuminated by the light from the light source; and comparison means for comparing a level of a read signal outputted from the reference member reading means to the shading correction data loaded down from the external device.
In the apparatus having the above configuration it is preferable to further comprise correction data setting means for transmitting an error signal to the external device as well as setting on-period data for the light source and shading correction data to the external device when it is determined by the comparison means that the level of the read signal outputted from the reference member reading means is lower than the signal level of the shading correction data loaded down from the external device.
According to still another aspect of the present invention, the foregoing object is attained by providing an image reading method capable of storing on-period data for a light source for irradiating light on an original and shading correction data for image data acquired by reading the original, in an external device, loading down the shading correction data from the external device at a beginning of image reading operation, and performing shading correction using the down-loaded shading correction data on the image data, the method comprising the steps of: controlling a turn-on/off operation of the light source in accordance with the on-period data down-loaded from the external device; reading light from a reference member illuminated with the light from the light source; and comparing a level of a read signal acquired in the reading step to a reference level of the shading correction data loaded down from the external device.
According to still another aspect of the present invention, the foregoing object is attained by providing an image reading method including the steps of: converting light from an original illuminated with light from a light source into electric signals; applying shading correction on the electric signals; communicating with an external device; and acquiring shading correction data used for the shading correction by reading light from a reference member, the method comprising the steps of: loading down on-period data for the light source and shading correction data set in the external device; controlling a turn-on/off operation of the light source on the basis of the down-loaded on-period data; reading the light from the reference member illuminated by the light from the light source; and comparing a level of a read signal acquired in the reading step to the shading correction data loaded down from the external device.
In the aforesaid method, it is preferable to further comprise a step of transmitting an error signal to the external device as well as setting on-period data for the light source and shading correction data to the external device when it is determined as a comparison result that the level of the read signal outputted from the reference member reading means is lower than the signal level of the shading correction data loaded down from the external device.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to perform the respective means of any of the image reading apparatuses as described above.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to execute any of the image reading methods as described above.
In accordance with the present invention as described above, after the apparatus is turned on and operation is initiated, an on-period of a light source and shading correction data which are set in an external device in advance are loaded down, and a reference level of the down-loaded shading correction data and a level of a signal newly obtained by reading reflected light from the reference member are compared.
In accordance with the present invention, it is preferable to transmit an error signal to the external device as well as set on-period data for the light source and shading correction data to the external device when it is determined that the level of the acquired signal by reading reflected light from the reference member is lower than the signal level of the shading correction data loaded down from the external device.
It is still another object of the present invention, to provide an image reading apparatus, an image reading method, and a storage medium capable of preventing image reading speed from being reduced caused by generating shading correction data for each image reading operation as well as generating shading correction data at proper timing without bothering a user.
According to one aspect of the present invention, the foregoing object is attained by providing an image reading apparatus comprising: photoelectric conversion means for converting an image read by scanning an original with light into analog electric signals; A/D conversion means for converting the analog electric signals outputted from the photoelectric conversion means into digital image data; image processing means for applying predetermined image processing to the digital image data outputted from the A/D conversion means; correction data generation means for generating shading correction data for performing shading correction on the digital image data by scanning and reading a reference original or a white board; correction data storage means for storing the shading correction data generated by the correction data generation means; correction means for performing the shading correction on the basis of the shading correction data generated by the correction data generation means; determination means for determining whether or not to generate the shading correction data; and control means for controlling whether or not to make the correction data generation means generate shading correction data, on the basis of a determination result by the determination means.
The determination means may have read number storage means for storing a number of times image reading operation is performed, and determines whether or not to generate the shading correction data on the basis of the number of times image reading operation is performed stored in the read number storage means.
Alternatively, the determination means may have time measurement means for measuring time elapsed since shading correction data has been generated last time, and determines whether or not to generate the shading correction data on the basis of a measurement result by the time measurement means.
According to another aspect of the present invention, the foregoing object is attained by providing an image reading method comprising the steps of: converting an image read by scanning an original with light into analog electric signals; converting the analog electric signals acquired by performing photoelectric conversion into digital image data; applying predetermined image processing to the digital image data; generating shading correction data for performing shading correction on the digital image data by scanning and reading a reference original or a white board; storing the generated shading correction data in a storage medium; performing the shading correction on the basis of the generated shading correction data; determining whether or not to generate the shading correction data; and controlling whether or not to generate shading correction data on the basis of a determination result.
In the determination step, a number of times image reading operation is performed may be stored in the storage medium, and whether or not to generate the shading correction data may be determined on the basis of the number of times image reading operation is performed stored in the storage medium.
Further, in the determination step, time elapsed since shading correction data was generated last time may be measured, and whether or not to generate the shading correction data may be determined on the basis of a measurement result.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to perform the respective means of any of the image reading apparatuses as described above.
According to still another aspect of the present invention, the foregoing object is attained by providing a storage medium for storing program codes which cause a computer to execute any of the image reading methods as described above.
In accordance with the present invention as described above, the shading correction data is automatically generated only when it is necessary to generate it for performing optimum shading correction.
The invention is particularly advantageous since it is possible to output image signals to which shading correction has been applied using a minimum memory area and a white shading correction board of a minimum width.
Further, when the level of a read signal does not reach a predetermined level because of deterioration of an LED, for instance, such cases can be detected. Accordingly, deterioration of the quality of a read image due to lack of illumination light is properly prevented; thus a proper shading correction is always performed and preferable image data can be obtained.
Furthermore, in a case where it is not proper to use shading correction data stored in an external device, the data is automatically updated, thereby latest shading correction data is always stored in the external device.
Further, new shading correction data is automatically generated only when the new data is needed, thus, it is possible to prevent time from being wasted for generating unnecessary shading correction data. Accordingly, throughput of an image reading operation is increased.
Further, the load on a user of making a decision on whether or not to generate shading correction data is reduced.